Whitsun — a curruption of "White Sunday", the usual name in Britain (though not now in Ireland) for Pentecost, the seventh Sunday after Easter. It was traditionally an occasion for young women of the parish to wear new white dresses attending church. ((Wikipedia.)) gauds — (("showy ceremonies, 'pomps and vanities'" now rhetorical – OED.))

moidering — ((moider: "perplex, worry, fatigue" – Slanguage.))

Badge of the Gaelic LeagueConnradh na Gaeghilge = League of the GaelsTir is Teanga = Country and Tongue

stuck in his lapel ... — the priest is wearing the badge of the Gaelic League.

uniformis — an apparent pun on "in uniform" and "uniformly", i.e. "looking alike" and "playing together". It's hard to see how the Latin uniformis can hang this together.

embrace of the Roman Empire — the Roman historian Tacitus recalls that his father-in-law Agricola, conqueror of Britain, often claimed that Ireland could be subdued with "a single legion and a few auxiliaries". Gibbon in a note remarks "The Irish writers, jealous of their national honour, are extremely provoked on this occasion, both with Tacitus and with Agricola" – Gibbon, Decline and Fall of the Roman Empire, 1782.